Surfactant adsorption to soil components and soils

Soil flushing for remediation of landfill leachate-contaminated soil: A comprehensive evaluation of optimal flushing agents and influencing factors

Screening the appropriate agent is essential to enhancing the effectiveness of soil flushing techniques in remediating landfill leachate contaminated soil. To identify effective flushing agents for leachate-contaminated soil and determine optimal conditions for their use, this study evaluated five surfactants and three chelating agents. These agents were analyzed through batch experiments and one-dimensional column tests to assess the effects of pH, temperature, solid-liquid ratio, and injection conditions on their efficacy. The findings revealed that saponin, known for its high degradability, was most effective in extracting heavy metals (total Cr and Cr (VI)), total nitrogen, ammonia nitrogen, and organic compounds. Notably, the removal efficiency of these contaminants by saponin increased with higher concentrations. Conversely, higher pH levels reduced the effectiveness of polysorbate 80 (Tween 80), rhamnolipid (RL), and saponin in removing chromium but improved ammonia nitrogen extraction. Alternatively, the remediation outcomes are also subject to a tight control of temperature and solid-liquid ratios, which is reflected in the strengthening efficiency along with rising temperatures and the amount of flushing agents applied. The study further examined the impact of different injection methods on the remediation process. Continuous injection was most effective for soils primarily contaminated with chromium, whereas a step-gradient mode yielded better results for nitrogen compounds. For soils with a high concentration of organic pollutants, a multi-pulse injection mode was optimal. These insights provide a solid foundation for developing targeted soil flushing strategies aimed at enhancing the remediation of soils contaminated by landfill leachate.

Adsorption characteristics of individual and binary mixture of ciprofloxacin antibiotic and lead(II) on synthesized bamboo-biochar

Adsorption of individual and a binary mixture of ciprofloxacin antibiotic (CFX) and lead ion, Pb(II) on bamboo biochar was investigated in this study. Bamboo biochar which was successfully fabricated by pyrolysis was carefully characterized by XRD, SEM, TEM, BET, FT-IR, XPS and zeta potential measurements to confirm the porous structure and high specific surface area of 134 m2 g-1. Individual and simultaneous adsorption of CFX and Pb(II) on synthesized bamboo biochar was systematically studied by batch technique. The optimum experimental parameters for CFX and Pb(II) simultaneous adsorption were pH 6, 5.0 mg mL-1 bamboo-biochar dosage, contact time 120 min while that were found to be, adsorbent dosage of 2.5 mg mL-1 and 60 min contact time, pH 3 for CFX and pH 4 for Pb(II) individual adsorption. The maximum adsorption efficiencies of binary mixture CFX and Pb(II) on bamboo biochar were achieved 99.9 and 90.8%, respectively while the very high adsorption capacities fitted by Langmuir model were found to be 183.6 and 285.7 mg g-1 for Pb(II) and CFX, respectively. Adsorption mechanisms of CFX and Pb(II) on bamboo biochar were discussed in details based on surface charge changes and isothermal data.

A hidden artefact: how surfactants can distort the results of springtail reproduction tests

Soils are exposed to multiple substance groups, including surfactants, which directly enter soils when they are used as additives in firefighting liquids or pesticide mixtures due to their surface tension-lowering properties. The impact of chemicals on soil health is often tested with the springtail reproduction test. We tested the effects of the trisiloxane Break-Thru® S 301 on the reproduction of Folsomia candida in three soils according to Organisation for Economic Co-operaton and Development (OECD) guideline 232. Juveniles were extracted either by heat or flotation. In the latter method, recommended by OECD 232, test soil is flooded with water and stirred so that springtails float and swim on the water surface. Additionally, we tested the impact of Break-Thru S 301 on other life-history endpoints linked with reproduction, namely, reproduction investment and hatching success. We found a significant decline of recovered springtails at soil concentrations of Break-Thru S 301 down to 2 mg/kg in sandy soils when using flotation. However, using heat extraction, no effects were found at the same concentrations. Also, reproduction investment and hatching success did not indicate any toxicity of Break-Thru S 301 to springtails at all. In conclusion, Break-Thru S 301 reduced the water surface tension in the flotation process so that springtail juveniles just sank and disappeared from the water surface. This artefact potentially can occur for all surfactants tested this way. We propose testing surfactant impact on springtail flotation by adding a few drops of surfactant and observing springtail sinking behavior before testing toxicity. Alternatively, heat extraction or surfactant controls can be applied. Most importantly, these options should be mentioned in the respective guidelines, which are highly relevant for chemical risk assessment.

Interaction of Pb(II) with microplastic-sediment complexes: Critical effect of surfactant

In this study, the impact of surfactants on the adsorption behavior of Pb(II) onto microplastics-sediment (MPs-S) complexes was investigated. Firstly, virgin polyamide (VPA) and polyethylene (VPE) were placed in Xiangjiang River sediment for six months to conduct in-situ aging. The results indicated that the biofilm-developed polyamide (BPA) and polyethylene (BPE) formed new oxygen-containing functional groups and different biofilm species. Furthermore, the adsorption capacity of Pb(II) in sediment (S) and MPs-S complexes was in the following order: S > BPA-S > VPE-S > VPA-S > BPE-S. The addition of sodium dodecyl benzenesulfonate (SDBS) promoted the adsorption of Pb(II), and the adsorption amount of Pb(II) increased with the higher concentration of SDBS, while adding cetyltrimethylammonium bromide (CTAB) showed the opposite result. The adsorption process of MPs-S complexes to Pb(II) was dominated by chemical adsorption, and the interaction between MPs-S complexes and Pb(II) was multilayer adsorption involving physical and chemical adsorption when the surfactants were added. Besides, the pH exerts a significant effect on Pb(II) adsorption in different MPs-S complexes, and the highest adsorption amount occurred at pH 6. Noteworthy, CTAB promoted the adsorption ability of Pb(II) when the exogenous FA was added. The binding characteristic of sediment endogenous DOM components and Pb(II) was influenced by the addition of MPs and surfactants. Finally, it confirmed that adsorption mechanisms mainly involve electrostatic and hydrophobic interaction. This study provides a new perspective to explore the environmental behaviors of Pb(II) by MPs and sediments with the addition of surfactants, which was conducive to evaluating the ecological risks of MPs and heavy metals in aquatic environments.

Surfactant-Based Chemical Washing to Remediate Oil-Contaminated Soil: The State of Knowledge

As the energy demand increases, there is a significant expansion and utilization of oil resources, resulting in the inevitable occurrence of environmental pollution. Oil has been identified as a prevalent soil contaminant, posing substantial risks to the soil ecosystems. The remediation of soil contaminated with oil is a formidable undertaking. Increasing evidence shows that chemical washing, a remediation technique employing chemical reagents like surfactants to augment the solubilization, desorption, and separation of petroleum hydrocarbons in soil, proves to be an efficacious approach, but the latest advances on this topic have not been systematically reviewed. Here, we present the state of knowledge about the surfactant-based chemical washing to remediate oil-contaminated soil. Using the latest data, the present article systematically summarizes the advancements on ex situ chemical washing of oil pollution and provides a concise summary of the underlying principles. The use of various surfactants in chemical washing and the factors influencing remediation efficiency are highlighted. Based on the current research status and knowledge gaps, future perspectives are proposed to facilitate chemical washing of oil-polluted soil. This review can help recognize the application of chemical washing in the remediation of oil-polluted soil.

Effect of cations on monochlorobenzene adsorption onto bentonite at the coexistence of Tween 80

The effect of several prevalent cations (including Na+, K+, Mg2+, Ca2+, Al3+, and Fe3+) on the adsorption of monochlorobenzene (MCB) onto bentonite was investigated at the coexistence of nonionic surfactant Tween 80 (T80) in surfactant-enhanced remediation (SER). They are all favorable for MCB and T80 adsorption, especially Mg2+ and Ca2+. Adsorption of MCB is strongly depended on T80 micelles. When its concentration exceeds the solubility, MCB is easier to bind with T80 micelles and be adsorbed by bentonite. Acidic environment can facilitate MCB and T80 adsorption, but the effect of cations on the adsorption is most significant under alkaline conditions. Adsorption capacity of MCB increases first followed by a slight decrease with increasing cations concentrations. The maximum adsorption rate of MCB determined is about 68.4% in a solution containing Mg2+ in the isothermal adsorption of MCB, while it is only 6.8% in a cation-free solution. Various characterizations showed that cations mainly changed the repulsion between bentonite particles and T80 micelles and the agglomeration and structure of bentonite, thus affecting the adsorption of MCB and T80 micelles. Our research demonstrated the nonnegligible promotion of MCB adsorption on bentonite by cations and acidic environment, which will adversely affect SER efficiency.

Enhancing biogas production from palm oil mill effluent through the synergistic application of surfactants and iron supplements

In this study, the effects of various surfactants on the soluble chemical oxygen demand (COD) fraction and biogas production from palm oil mill effluent (POME) were investigated. A cationic surfactant (cetyltrimethylammonium bromide, CTAB) and a nonionic surfactant (Tween 80; TW80) were found to adsorb onto the particulate matter from POME, markedly reducing the soluble COD, unlike an anionic surfactant (sodium dodecyl sulfate, SDS). The mechanism underlying this phenomenon might be the adsolubilization of oil on particulate matter induced by the adsorbed surfactants. In terms of biogas production, 0.1 % w/v SDS and CTAB dramatically reduced the biogas yield, while 0.1 % w/v TW80 did not have this negative effect. A synergistic effect was observed when TW80 (0.1 % w/v) was combined with FeSO4 (400 mg/L), resulting in a 17 % greater biogas yield than that achieved with treatments using TW80 or FeSO4 alone. Moreover, the combination of TW80 and FeSO4 increased the biogas production rate. Surprisingly, the water-soluble iron fraction remained consistent across all treatments, suggesting that the adsorption of TW80 on particulate matter may limit micelle formation. Importantly, the proportion of methane in the generated biogas remained stable in all the treatments. Microbial community analysis revealed that the introduction of TW80 and FeSO4 had no discernible impact on the microbial community of the system. Pretreatment with TW80 and an iron supplement significantly enhanced biogas production and reduced the retention time of the anaerobic digestion (AD) system while maintaining the biogas quality and microbial community stability.

Adsorption behavior and the potential risk of As(V) in soils: exploring the effects of representative surfactants

Arsenic contamination in soils poses a critical global challenge, yet the influence of surfactants on arsenic adsorption behavior is often underestimated. This study aims to investigate the effects of three representative surfactants, namely cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyethylene glycol anhydrous sugar alcohol monooleate (Tween 80), on arsenic adsorption behavior in soils. The adsorption isotherm shifts from a single Temkin model without surfactants to both the Langmuir and Temkin models in the presence of surfactants, indicating the simultaneous occurrence of monolayer and multilayer adsorption for arsenic in soils. Moreover, the surfactants can inhibit the adsorption and hasten the attainment of adsorption equilibrium. SDS displayed the most inhibitory effect on arsenic adsorption, followed by Tween 80 and CTAB, due to the competitive adsorption, electrostatic interaction, and hydrophobic interaction. Variations in zeta potential with different surfactants further elucidate this inhibitory phenomenon. Through orthogonal experiment analyses, pH emerges as a primary factor influencing arsenic adsorption in soils, with surfactant concentration and type identified as secondary factors. Temperature notably affects CTAB, with the adsorption inhibition rate plummeting to a mere 0.88% at 50 °C. Sequential extraction analysis revealed that surfactants enhanced the bioavailability of arsenic. The FTIR, XRD, SEM, and CA analyses further support the mechanism underlying the effect of surfactants on arsenic adsorption in soil. These analyses indicate that surfactants modify the composition and abundance of functional groups, hinder the formation of arsenic-containing substances, and improve soil compactness, smoothness, and hydrophilicity. This study provides valuable insights into the effect of surfactants in arsenic-contaminated soils, which is often ignored in previous work.

Changes in soil organic carbon stocks and its physical fractions along an elevation in a subtropical mountain forest

Soil microorganisms are the drivers of soil organic carbon (SOC) mineralization, and the activities of these microorganisms are considered to play a key role in SOC dynamics. However, studies of the relationship between soil microbial carbon metabolism and SOC stocks are rare, especially in different physical fractions (e.g., particulate organic carbon (POC) fraction and mineral-associated organic carbon (MAOC) fraction). In this study, we investigated the changing patterns of SOC stocks, POC stocks, MAOC stocks and microbial carbon metabolism (e.g., microbial growth, carbon use efficiency and biomass turnover time) at 0-20 cm along an elevational gradient in a subtropical mountain forest ecosystem. Our results showed that SOC and POC stocks increased but MAOC stocks remained stable along the elevational gradient. Soil microbial growth increased while microbial turnover time decreased with elevation. Using structural equation modeling, we found that heightened microbial growth is associated with elevated POC stocks. Moreover, MAOC stocks positively correlate with microbial growth but show negative associations with both POC stocks and soil pH. Overall, the increase in SOC stocks along the elevational gradient is primarily driven by changes in POC stocks rather than MAOC stocks. These findings underscore the importance of considering diverse soil carbon fractions and microbial activities in predicting SOC responses to elevation, offering insights into potential climate change feedbacks.

A novel eco-friendly strategy for removing phenanthrene from groundwater: Synergism of nanobubbles and rhamnolipid

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %-19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

Surfactant-Mediated Effects on Hydrological and Physical Soil Properties: Data Synthesis

Soils are under the threat of a multitude of anthropogenic factors affecting the complex interplay of various physical and hydrological soil processes and properties. One such factor is the group of surface-active compounds. Surfactants have a broad range of applications and can reduce solid-liquid interfacial forces and increase wettability and dispersion of particles. Surfactant effects are context-dependent, giving rise to a wide range of reported effects on different soil processes and properties. Here, we evaluate the evidence base of surfactant research on 11 hydrological and physical soil variables. Our goal was to identify knowledge gaps and test the robustness of the proposed surfactant effects. We found that the current knowledge base is insufficient to reach strong data-backed conclusions about the effects of surfactants in soils. We identified a unique case of bias in the data as a result of conflated patterns from laboratory and field studies. We could not support the hypothesis that the surfactant charge determines soil effects for any of the tested soil variables. We believe that further experiments on surfactant-mediated effects on soil properties and processes are urgently required, paying attention, in particular, to improving experimental design and data reporting standards.

Surfactant-enhanced anoxic degradation of polycyclic aromatic hydrocarbons (PAHs) in aged subsurface soil at high temperature (60 °C)

Thermally enhanced anoxic biodegradation is emerging as a promising method for removing PAHs from subsurface soil. However, some PAHs still remain in soil following remediation with thermally enhanced anoxic degradation due to low bioavailability of these residual PAHs. The effects of five surfactants (Tween 80, TX 100, Brij 30, SDS, and SDBS) on the desorption of PAHs, anoxic degradation of PAHs, and native bacteria in soil at high temperature (60 °C) were evaluated in this study. The desorption of PAHs in soil increased as surfactant concentration increased. Low doses of surfactants (0.08%, w/w) enhanced the growth of potential PAHs degrading bacteria and promoted the anoxic degradation of PAHs, whereas high doses of surfactants (0.3%-0.8%, w/w) displayed the opposite effect, and the degree of inhibition increased with increasing surfactant concentration. The results also indicated that the inhibitory effect of anionic surfactants (SDS and SDBS) on microbial growth and PAHs degradation is stronger than that of nonionic surfactants (Tween 80, TX 100 and Brij 30) at the same concentration. These results suggest a feasible way of enhancing the anoxic degradation of PAHs in soil where heat cannot be effectively utilized when in situ thermal desorption (ISTD) technology is used.

Sorption of ionic liquids in soil enriched with polystyrene microplastic reveals independent behavior of cations and anions

Recently, much attention has been focused on the application of the Ionic Liquids (ILs) with herbicidal activity in agriculture. It has been suggested that through the appropriate selection of cations and anions, one can adjust the properties of ILs, particularly the hydrophobicity, solubility, bioavailability, toxicity. In practical agricultural conditions, it will be beneficial to reduce the mobility of herbicidal anions, such as the commonly applied 2,4-dichlorophenoxyacetic acid [2,4-D] in the soil. Furthermore, microplastics are becoming increasingly prevalent in the soil, potentially stimulating herbicidal sorption. Therefore, we investigated whether cations in ILs influence the mobility of anions in OECD soil supplemented with polystyrene microplastic (PS). For this purpose, we used the 2,4-D based ILs consisting of: a hydrophilic choline cation [Chol][2,4-D] and a hydrophobic choline cation with a C12chain [C12Chol][2,4-D]. Characterization of selected micropolystyrene was carried out using the BET sorption-desorption isotherm, particle size distribution and changes in soil sorption parameters such as soil sorption capacity and cation exchange capacity. Based on the batch sorption experiment, the effect of microplastic on the sorption of individual cations and anions in soil contaminated with micropolystyrene was evaluated. The results obtained indicate that the introduction of a 1-10% (w/w) PS resulted in an 18-23% increase of the soil sorption capacity. However, the sorption of both ILs' cations increased only by 3-5%. No sorption of the [2,4-D] anion was noted. This suggests that cations and anions forming ILs, behave independently of each other in the environment. The results indicate the fact that ILs upon introduction into the environment are not a new type of emerging contaminant, but rather a typical mixture of ions. It is worth noting that when analyzing the behavior of ILs in the environment, it is necessary to follow the fate of both cations and anions.

Preparation, characteristics, and performance of the microemulsion system in the removal of oil from beach sand

Oil deposited on shoreline substrates has serious adverse effects on the coastal environment and can persist for a long time. In this study, a green and effective microemulsion (ME) derived from vegetable oil was developed as a washing fluid to remove stranded oil from beach sand. The pseudo-ternary phase diagrams of the castor oil/water (without or without NaCl)/Triton X-100/ethanol were constructed to determine ME regions, and they also demonstrated that the phase behaviors of ME systems were almost independent of salinity. ME-A and ME-B exhibited high oil removal performance, low surfactant residues, and economic benefits, which were determined to be the W/O microstructure. Under optimal operation conditions, the oil removal efficiencies for both ME systems were 84.3 % and 86.8 %, respectively. Moreover, the reusability evaluation showed that the ME system still had over 70 % oil removal rates, even though it was used six times, implying its sustainability and reliability.

Influence of Henna Extracts on Static and Dynamic Adsorption of Sodium Dodecyl Sulfate and Residual Oil Recovery from Quartz Sand

The application of surfactant flooding for enhanced oil recovery (EOR) promotes hydrocarbon recovery through reduction of oil-water interfacial tension and alteration of oil-wet rock wettability into the water-wet state. Unfortunately, surfactant depletion in porous media, due to surfactant molecule adsorption and retention, adversely affects oil recovery, thus increasing the cost of the surfactant flooding process. Chemical-based materials are normally used as inhibitors or sacrificial agents to minimize surfactant adsorption, but they are quite expensive and not environmentally friendly. Plant-based materials (henna extracts) are far more sustainable because they are obtained from natural sources. However, there is limited research on the application of henna extracts as inhibitors to reduce dynamic adsorption of the surfactant in porous media and improve oil recovery from such media. Thus, henna extracts were introduced as an eco-friendly and low-cost sacrificial agent for minimizing the static and dynamic adsorption of sodium dodecyl sulfate (SDS) onto quartz sand in this study. Results showed that the extent of surfactant adsorption was inversely proportional to the henna extract concentration, and the adsorption of the henna extract onto the quartz surface was a multilayer adsorption that followed the Freundlich isotherm model. Precisely, the henna extract adsorption on quartz sand is in the range of 3.12-4.48 mg/g (for static adsorption) and 5.49-6.73 mg/g (for dynamic adsorption), whereas the SDS adsorption on quartz sand was obtained as 2.11 and 4.79 mg/g at static and dynamic conditions, respectively. In the presence of 8000 mg/L henna extract, SDS static and dynamic adsorption was significantly reduced by 64 and 82%, respectively. At the same conditions, the residual oil recovery increased by 9.2% over normal surfactant flooding. The study suggests that the use of henna extracts as a sacrificial agent during SDS flooding could result in the reduction of static and dynamic adsorption of surfactant molecules on quartz sand, thus promoting hydrocarbon recovery from sandstone formations.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

An Overview on the Treatment of Oil Pollutants in Soil Using Synthetic and Biological Surfactant Foam and Nanoparticles

Oil-contaminated soil is one of the most concerning problems due to its potential damage to human, animals, and the environment. Nanoparticles have effectively been used to degrade oil pollution in soil in the lab and in the field for a long time. In recent years, surfactant foam and nanoparticles have shown high removal of oil pollutants from contaminated soil. This review provides an overview on the remediation of oil pollutants in soil using nanoparticles, surfactant foams, and nanoparticle-stabilized surfactant foams. In particular, the fate and transport of oil compounds in the soil, the interaction of nanoparticles and surfactant foam, the removal mechanisms of nanoparticles and various surfactant foams, the effect of some factors (e.g., soil characteristics and amount, nanoparticle properties, surfactant concentration) on remediation efficiency, and some advantages and disadvantages of these methods are evaluated. Different nanoparticles and surfactant foam can be effectively utilized for treating oil compounds in contaminated soil. The treatment efficiency is dependent on many factors. Thus, optimizing these factors in each scenario is required to achieve a high remediation rate while not causing negative effects on humans, animals, and the environment. In the future, more research on the soil types, operating cost, posttreatment process, and recycling and reuse of surfactants and nanoparticles need to be conducted.

Polycyclic aromatic hydrocarbons remobilization from contaminated porous media by (bio)surfactants washing

Biosurfactants, surface-active agents produced by microorganisms, are increasingly studied for their potential use in soil remediation processes because they are more environmentally friendly than their chemically produced homologues. In this work, we report on the use of a crude biosurfactant produced by a bacterial consortium isolated from a PAHs-contaminated soil, compared with other (bio)surfactants (Tween80, Sodium dodecyl sulfate - SDS, rhamnolipids mix), to wash PAHs from a contaminated porous media. Assays were done using columns filled with sand or sand-clay mixtures (95:5) spiked with four model PAHs. The crude biosurfactant showed less adsorption to the [sand] and the [sand + clay] columns compared to Tween 80, SDS and the rhamnolipid mix. The biosurfactant showed the second best capacity to remove PAHs from the columns (as dissolved and particulate phases), both from [sand] and [sand + clay], after SDS when applied at lower concentrations than the other sufactants. The effluent concentrations of phenanthrene (PHE), pyrene (PYR) and benzo[a]pyrene (BAP) increased in the presence of the crude biosurfactant. Compared to the control experiment using only water, the global PAHs washed mass (amount of PAHs removed from the columns) increased between 9 and 1000 times for PHE and BAP in the [sand] column, and between 55 and 6000 times respectively for PHE and BAP in the [sand + clay] columns. Moreover, in the [sand + clay] columns, leaching of a part of the clays was observed in the SDS and the biosurfactant injections assays. This clay leaching resulted in higher PAHs removal, due not to desorption but rather to particulate transport. In the context of washing PAH-contaminated soils in biopiles or subsurface remediation, our results could help in sizing the remediation approach using an environmental friendly biosurfactant, before a pump-and-treat process.

Ecological Risk Analysis for Benzalkonium Chloride, Benzethonium Chloride, and Chloroxylenol in US Disinfecting and Sanitizing Products

Use of three topical antiseptic compounds-benzalkonium chloride (BAC), benzethonium chloride (BZT), and chloroxylenol (PCMX)-has recently increased because of the phaseout of other antimicrobial ingredients (such as triclosan) in soaps and other disinfecting and sanitizing products. Further, use of sanitizing products in general increased during the coronavirus (COVID-19) pandemic. We assessed the environmental safety of BAC, BZT, and PCMX based on best available environmental fate and effects data from the scientific literature and privately held sources. The ecological exposure assessment focused on aquatic systems receiving effluent from wastewater-treatment plants (WWTPs) and terrestrial systems receiving land-applied WWTP biosolids. Recent exposure levels were characterized based on environmental monitoring data supplemented by modeling, while future exposures were modeled based on a hypothetical triclosan replacement scenario. Hazard profiles were developed based on acute and chronic studies examining toxicity to aquatic life (fish, invertebrates, algae, vascular plants) and terrestrial endpoints (plants, soil invertebrates, and microbial functions related to soil fertility). Risks to higher trophic levels were not assessed because these compounds are not appreciably bioaccumulative. The risk analysis indicated that neither BZT nor PCMX in any exposure media is likely to cause adverse ecological effects under the exposure scenarios assessed in the present study. Under these scenarios, total BAC exposures are at least three times less than estimated effect thresholds, while margins of safety for freely dissolved BAC are estimated to be greater than an order of magnitude. Because the modeling did not specifically account for COVID-19 pandemic-related usage, further environmental monitoring is anticipated to understand potential changes in environmental exposures as a result of increased antiseptic use. The analysis presented provides a framework to interpret future antiseptic monitoring results, including monitoring parameters and modeling approaches to address bioavailability of the chemicals of interest. Environ Toxicol Chem 2022;41:3095-3115. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Plant-derived saponin enhances biodegradation of petroleum hydrocarbons in the rhizosphere of native wild plants

Plant-derived saponins are bioactive surfactant compounds that can solubilize organic pollutants in environmental matrices, thereby facilitating pollutant remediation. Externally applied saponin has potential to enhance total petroleum hydrocarbon (TPH) biodegradation in the root zone (rhizosphere) of wild plants, but the associated mechanisms are not well understood. For the first time, this study evaluated a triterpenoid saponin (from red ash leaves, Alphitonia excelsa) in comparison to a synthetic surfactant (Triton X-100) for their effects on plant growth and biodegradation of TPH in the rhizosphere of two native wild species (a grass, Chloris truncata, and a shrub, Hakea prostrata). The addition of Triton X-100 at the highest level (1000 mg/kg) in the polluted soil significantly hindered the plant growth (reduced plant biomass and photosynthesis) and associated rhizosphere microbial activity in both the studied plants. Therefore, TPH removal in the rhizosphere of both plant species treated with the synthetic surfactant was not enhanced (at the lower level, 500 mg/kg soil) and even slightly decreased (at the highest level) compared to that in the surfactant-free (control) treatment. By contrast, TPH removal was significantly increased with saponin application (up to 60% in C. truncata at 1000 mg/kg due to enhanced plant growth and associated rhizosphere microbial activity). No significant difference was observed between the two saponin application levels. Dehydrogenase activity positively correlated with TPH removal (p < 0.001) and thus this parameter could be used as an indicator to predict the rhizoremediation efficiency. This work indicates that saponin-amended rhizoremediation could be an environmentally friendly and effective biological approach to remediate TPH-polluted soils. It was clear that the enhanced plant growth and rhizosphere microbial activity played a crucial role in TPH rhizoremediation efficiency. The saponin-induced molecular processes that promoted plant growth and soil microbial activity in the rhizosphere warrant further studies.

Effect of humic acid on lysozyme interaction with montmorillonite and kaolinite

Humic acid (HA) as a soil natural organic matter (NOM) can participate in the interaction between proteins and clay minerals, depending on clay type, HA and protein content, and solution conditions. The effect of HA on the interaction of lysozyme (LSZ) with kaolinite (Kao) and montmorillonite (Mont) was investigated at (initial) pH_i 5 and 8. In the solutions containing both HA and LSZ, HA/LSZ complexes were formed with a net charge density depending on pH and HA/LSZ mass ratio f. LSZ adsorption on clays in the presence of HA is dominated by adsorption of HA/LSZ complexes. The HA/LSZ mass ratio (f_IEP,pHi) at the isoelectric point (IEP) is pH dependent. At f <f_IEP,pHi the HA/LSZ complexes are positively charged and adsorb well to the negatively charged Mont and Kao surface fractions. The adsorption levels on Mont are considerably larger than on Kao, which is mainly due to the much larger area fraction of modestly hydrophobic basal plates of Mont. The presence of HA increased the plateau adsorption of LSZ on Kao and Mont for both pH_i values, and the LSZ adsorption increased with increasing HA content and pH_i values due to a decreasing mutual repulsion of the bound HA/LSZ complexes. At pH_i 8 complications arose for low initial LSZ concentrations, for f <f_IEP,pHi the HA/LSZ complexes were only weakly positive and formed dispersed aggregates and for f >f_IEP,pHi the HA/LSZ complexes were negative, both conditions caused relatively high equilibrium concentrations of LSZ in solution that decreased with increasing initial LSZ concentration. The present results enhance our insight in protein soil interactions for the case that clay particles are brought in contact with aqueous solutions that contain modest amounts of both NOM and protein and stress the importance of the NOM/protein mass ratio and solution pH.

Effects of three surfactants on the degradation and environmental risk of metolachlor in aquatic environment

Surfactants and pesticides can be simultaneously detected in the environment by the reason of their widespread use and large amounts of emissions. Due to the special amphipathicity of surfactants, it may have special effects on the environmental behaviors and toxic effects of other substances in the environment. There are few relevant studies at present. In this study, the effects of three surfactants on the degradation of the amide pesticide metolachlor in water-sediment system were investigated. The study found that the three surfactants had no significant effect on the degradation of metolachlor in the system at environmental concentrations. However, at critical micelle concentration, cationic surfactant octadecyl trimethyl ammonium bromide and nonionic surfactant nonylphenol polyoxyethylene ether promoted the degradation of metolachlor in water-sediment system. Anionic surfactant odium dodecylbenzene sulfonate (SDBS) prolonged the degradation half-life of metolachlor. The presence of surfactants not only affected the environmental behavior of pesticides. When they coexisted with pesticides, the joint toxicity to aquatic organisms cannot be ignored. This study found that the combined effects of three surfactants and metolachlor on the acute developmental toxicity of zebrafish embryos were all synergistic effects. The combined effects of two ionic surfactants and metolachlor on the acute toxicity of adult zebrafish were synergistic effects. Further study showed that co-exposure of SDBS and metolachlor increased the absorption of metolachlor by zebrafish. Combined exposure of SDBS and metolachlor caused oxidative stress in brain, gill and liver of zebrafish. The results showed that the simultaneous presence of anionic surfactants and pesticides in the environment may increase the environmental risk of pesticides.

A simple empirical model for phenanthrene adsorption on soil clay minerals

Soil clay minerals are effective substrate adsorbents of polycyclic aromatic hydrocarbons (PAHs) in natural soil. The adsorbed PAHs result in long-term contamination of soils. In this paper, a typical PAH phenanthrene (Phe) and nine high purity clay minerals are selected as representative PAH pollutants and adsorbents, respectively. A series of experiments have been conducted to disclose the relationship between the Phe adsorption effect of these clay minerals and their physical properties, including specific surface area (SSA), cation exchange capacity (CEC) and contact angle (CA). Molecular simulation methods are performed to explore the mechanism of clay mineral structure on Phe adsorption at the molecular level. Density functional theory (DFT) calculation suggests that the adsorption of Phe on clay minerals is mainly due to the van der Waals effect. The strength of the O-H-π effect is greater than that of the hydrophobic effect of Phe adsorption. Molecular dynamic (MD) simulations imply that the hydration effect of cations hinders the Phe hydrophobic adsorption by occupying the adsorption sites. Based on the mechanism explored, a simple empirical model is proposed, and the adsorption distribution coefficient K_d of clay mineral and water phases can be precisely predicted by the three physical properties of clay minerals, without rigorous quantitative analysis of soil clay minerals.

Guidelines for surfactant selection to treat petroleum hydrocarbon-contaminated soils

The present study determined the most effective surfactants to remediate gasoline and diesel-contaminated soil integrating information from soil texture and soil organic matter. Different ranges for aliphatic and aromatic hydrocarbons (> C6-C8, > C8-C10, > C10-C12, > C12-C16, > C16-C21, and > C21-C35) in gasoline and diesel fuel were analyzed. This type of analysis has been investigated infrequently. Three types of soils (silty clay, silt loam, and loamy sand) and four surfactants (non-ionic: Brij 35 and Tween 80; anionic: SDBS and SDS) were used. The results indicated that the largest hydrocarbon desorption was 56% for silty clay soil (SDS), 59% for silt loam soil (SDBS), and 69% for loamy sand soil (SDS). Soils with large amounts of small particles showed the worst desorption efficiencies. Anionic surfactants removed more hydrocarbons than non-ionic surfactants. It was notable that preferential desorption on different hydrocarbon ranges was observed since aliphatic hydrocarbons and large ranges were the most recalcitrant compounds of gasoline and diesel fuel components. Unlike soil texture, natural organic matter concentration caused minor changes in the hydrocarbon removal rates. Based on these results, this study might be useful as a tool to select the most cost-effective surfactant knowing the soil texture and the size and chemical structure of the hydrocarbons present in a contaminated site.

Soil water solutes reduce the critical micelle concentration of quaternary ammonium compounds

Quaternary alkyl ammonium compounds (QAACs) are produced in large quantities for use as surfactants and disinfectants and also found in soils, sediments, and surface waters, where they are potentially involved in the selection of antibiotic resistance genes. Micelle formation influences fate and effects of QAACs. The critical micelle concentration (CMC) of six homologs of benzylalkylammonium chlorides (BAC) was determined in deionized water, 0.01 M CaCl₂ solution, and aqueous soil extracts, using both spectrofluorometric and tensiometric methods. Additionally, eight organic model compounds were employed at concentrations of 15 mg C L^-1 as background solutes in order to test the effect of dissolved organic carbon (DOC) on CMCs. Results found CMCs decreased with an increasing length of the alkyl chain from 188 mM for BAC-C8 to 0.1 mM for BAC-C18. Both methods yielded similar results for measurements in water and CaCl₂ solution; however, the spectrofluorescence method did not work for soil extracts due to fluorescence quenching phenomena. In soil extracts, CMCs of BAC-C12 were reduced below 3.7 mM, while the CMC reduction in soil extracts was less pronounced for BAC-C16. Besides ionic strength, molecular structures of BACs and dissolved organic compounds also affected the CMC. The number of carboxyl groups and small molecular weights of the DOC model compounds reduced the CMCs of BAC-C12 and BAC-C16 at pH 6. This study highlights that CMCs can be surpassed in soil solution, pore waters of sediments, or other natural waters even at (small) concentrations of QAACs typically found in the environment.

Two-step adsorption model for Pb ion accumulation at the algae-water interface in the presence of fulvic acid

The effects of fulvic acid (FA) on heavy metal bioaccumulation by algae have been extensively studied, but the quantitative description on its adsorption behavior is not elaborately illustrated. In the study, the two-step adsorption model is firstly proposed to describe the adsorption of Pb by algae in the presence of FA (R² > 0.984), which is characterized with two-plateaus in the biosorption curves. The first plateau in the curve represents a monolayer adsorption process of free Pb²⁺; while the second reveals a multilayer adsorption process of Pb-FA binding to those adsorbed Pb by algae, and the bonding material was called as ternary complex of algae-Pb-(FA-Pb). The formation of the ternary complex caused a sharp increase of the amount of adsorbed Pb by algae which was measured by an atomic absorption spectrophotometry, and a decrease of the toxicity of Pb to algae verified with SEM and TEM images. The ternary phase diagram showed FA could participate in the formation of ternary complexes at very low concentration. The study is important for a comprehensive understanding of the metal-microalgae interaction and its biogeochemical cycle in surface waters.

Nonionic and anionic surfactant-washing of polycyclic aromatic hydrocarbons in estuarine sediments around an industrial harbor in southern Taiwan

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (K_ow, K_oc and S_w) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.

Effects of homemade biosurfactant from Bacillus methylotrophicus on bioremediation efficiency of a clay soil contaminated with diesel oil

Despite constant progress in the understanding of the mechanisms related to the effects of biosurfactants in the bioremediation processes of oily residues, the possibility of antagonist effects on microbial growth and the production in situ of these compounds must be elucidated. The aims of this work were a) to evaluate the effects of the addition of a homemade biosurfactant of Bacillus methylotrophicus on the microbial count in soil in order to determine the possibility of inhibitory effects, and b) to accomplish biostimulation using media prepared with whey and bioaugmentation with B. methylotrophicus, analyzing the effects on the bioremediation of diesel oil and evidencing the in situ production of biosurfactants through effects on surface tension. The homemade bacterial biosurfactant did not present inhibitory effects acting as a biostimulant until 4000 mg biosurfactant/kg of soil. The biostimulation and bioaugmentation presented similar better results (p > 0.05) with the degradation of oil (~60%) than natural attenuation due to the low quantities of biostimulants added. For bioaugmentated and biostimulated soils, a decrease of surface tension between 30 and 60 days was observed, indicating the production of tensoactives in the soil, which was not observed in natural attenuation or a control treatment.

Comparison of Same Carbon Chain Length Cationic and Anionic Surfactant Adsorption on Silica

Adsorption of a cationic surfactant dodecyl pyridinium chloride (DPC) on silica was studied to show a comparison with the adsorption of an anionic surfactant sodium dodecyl sulfate (SDS), whose carbon chain length is the same and on the same silica. Results provided a better understanding of the adsorption mechanism of cationic and anionic surfactant on negatively charged silica. The experiment covered different electrolyte concentrations and pH values. Results indicated that at the same pH, the DPC adsorption amounts are higher when the electrolyte concentration is higher; at a higher DPC equilibrium concentration, the adsorption amount difference is larger than that at low DPC equilibrium concentration, and when DPC equilibrium concentration is lower than 0.1 mmol/L, the adsorption amount difference cannot be observed. At charge compensation point (CCP, 0 zeta potential), the negative surface charge of silica was compensated by DP+, a continuous increasing zeta potential indicated a bilayer adsorption of DPC on silica. The adsorption amount increased with increasing pH. The calculated lines by Gu and Zhu model show a two-step property, including a bilayer and hemi-micelle adsorption. DPC adsorbed more strongly on silica than SDS due to the combination of electrostatic and hydrophobic attraction.

Separation and determination of alkyl sulfate surfactants in wastewater by capillary electrophoresis coupled with contactless conductivity detection after preconcentration by simultaneous adsorption using alumina beads

The aim of the present study is to determine four anionic alkyl sulfate (AS) surfactants with different alkyl chains, namely, C8, C10, C12, and C14, in wastewater by CE with capacitively coupled contactless conductivity detection (CE-C⁴ D). The conditions effective for the separation of the four AS surfactants were systematically optimized and found to be in a Tris-His (50 mM/20 mM) BGE solution at a pH of 8.95, using a separation voltage of +15 kV, hydrodynamic injection by siphoning using a 20 cm injection height and an injection time of 20 s. The LODs for C8, C10, C12, and C14 were 2.58, 2.30, 2.08, and 3.16 mg/L, respectively. The conditions used to achieve the simultaneous adsorption and preconcentration of the AS surfactants using Al₂ O₃ beads were pH of 3 and 0.1 mM NaCl. The adsorption efficiencies were found to be 45.6, 50.8, 81.7, and 99.9%, while the desorption efficiencies reached 66.1, 70.4, 83.9, and 100.0% for C8, C10, C12, and C14, respectively. The concentrations of the AS surfactants in wastewater samples were quantified by CE-C⁴ D after preconcentration by simultaneous adsorption using Al₂ O₃ beads. The results obtained from the proposed method were consistent with those obtained by HPLC-MS/MS, with a deviation of less than 15%. Our results indicate that the CE-C⁴ D performed after preconcentration by an adsorption technique using Al₂ O₃ beads is a new, inexpensive, and suitable method for quantifying AS surfactants in wastewater samples.

Single and competitive sorption of sulfadiazine and chlortetracycline on loess soil from Northwest China☆

The fate of veterinary antibiotics (VAs) in soil environment is determined by the hydrophilic performance and solubility of VAs and the type of soil. In this study, sulfadiazine (SDZ) and chlortetracycline (CTC) were selected as target pollutants, and a batch sorption method was used to find out the single and sorption competitive behavior and mechanism of the target pollutants on loess soil. Kinetic studies showed the apparent sorption equilibrium was reached 0-6 h for CTC and 0-12 h for SDZ. The sorption kinetics of VAs on loess soil were fitted well with a pseudo-second order kinetic model. Sorption thermodynamic data indicated the isotherm sorption of both SDZ and CTC on loess soil was fitted well with Freundlich isothermal (R², 0.960-0.975) and linear models (R², 0.908-0.976). The sorption affinity of CTC (K_d, 290-1620 L/kg for CTC) was much greater than that of SDZ (K_d, 0.6-4.9 L/kg for SDZ). The results also suggest that SDZ may be easily mobilized or leached from loess soil at neutral and alkaline pH, while CTC may be easily mobilized or leached at neutral pH. The sorption of each single target pollutant on the outer layer complex decreased with increasing ionic strength. Higher initial concentrations resulted in greater sorption capacity of target pollutants on loess soil increased. The sorption capacities of CTC and SDZ in the mixed system were lower than the sorption capacity of each single system, showing a competitive sorption behavior of CTC and SDZ during the sorption process. Overall, CTC showed the highest sorption potential in loess soil, whereas SDZ showed a high leaching risk in loess soil. These findings contribute to understanding the fate of different VAs in loess in the natural environment.

XPS and two-dimensional FTIR correlation analysis on the binding characteristics of humic acid onto kaolinite surface

The stabilization and preservation of soil organic matter have been attributed to the strong reactive sites of mineral surfaces that cause physical isolation and chemical stabilization due to the organic-mineral interface. However, much of the micro-scale knowledge about interactions between organic ligands and minerals largely remains at the qualitative level, and neglects the heterogeneity of functional groups of organic matter. Here, we report the use of molecular-scale technologies of two-dimensional FTIR Correlation Spectroscopy (2D-FTIR-CoS) and X-ray Photoelectron Spectroscopy (XPS) to directly measure the binding processes of humic acid (JGHA) groups onto kaolinite surface. The spectroscopy results showed that the carboxylate groups, aliphatic OH and aromatic structure participate in the binding of JGHA on kaolinite surface. The carboxylic and phenolic hydroxyl interact with kaolinite surface through the interfacial COAl/Si bonds. Kaolinite prefers to adsorb C-groups at pH 4.0 and O-groups at pH 8.0. The interaction of COO^- group at 1566 cm^-1 of JGHA leads to the formation of inner-sphere complex first and then outer-sphere complex with increasing contact time. The interaction of COOH group at 1261 cm^-1 with the AlOH²⁺ of kaolinite was could be ascribed to ligand exchange and/or electrostatic attraction, whose contribution was evaluated to be 13.90%, 7.65% and 0% at pH 4.0, 6.0 and 8.0, respectively. These results of molecular binding provide quantitative mechanistic insights into organic-mineral interactions and expound the effect of functional groups of HA on binding mechanisms, and thus bring important clues for better understanding the mobility and transformation of land‑carbon including mineral-bound carbon.

Equilibrium mono- and multicomponent adsorption models: From homogeneous ideal to heterogeneous non-ideal binding

Aqueous sorption processes play an important role in, for example, pollutant binding to natural nanoparticles, colloid stability, separation and enrichment of components and remediation processes. In this article, which is a tribute to Hans Lyklema, models of localized (ad)sorption of molecules and ions from aqueous solution on homogeneous and heterogeneous nanoparticles are presented. The discussed models range from ideal monocomponent sorption on homogeneous (Langmuir) and heterogeneous sites, to multicomponent ideal sorption on homogeneous and heterogeneous sites, multicomponent multisite ion complexation with charge distribution (CD-MUSIC) and non-ideal competitive adsorption on heterogeneous sites (NICA). Attention is also paid to lateral interaction, site-induced aggregation, binding stoichiometry and multilayer formation. Electrical double layer models are discussed in relation to ion binding on impermeable and permeable nanoparticles. Insight in models that can describe sorption of molecules and ions on nanoparticles leads to awareness of the limitations of using simple models for complex systems and is needed for the selection and application of an appropriate model for a given system. This is relevant for all practical sorption processes and for a better understanding of the role of natural nanoparticles in the binding of nutrients and pollutants.

Sorption of surfactants onto sediment at environmentally relevant concentrations: independent-mode as unifying concept

At low surfactant concentrations often non-linear sorption processes are observed when natural adsorbents like sediment or soil are involved. This sorption process is often explained by a Dual-Model (DM) model, which assumes sorption to an adsorbent to be based on a combined ionic-polar and non-polar sorption interaction term. An Independent-Mode (IM) model, however, could treat surfactant sorption as two independent sorption processes to which the non-polar and ionic-polar features of the surfactant molecule contribute differently. For both models the overall exact partition coefficient, K, and its corresponding total standard free enthalpy of adsorption, Δ_sG, are derived. We tested the outcome of both models against multiple published experimental sorption data sets by, (i) varying the organic carbon fraction, (ii) constructing sorption and partition isotherms over different concentration ranges, (iii) removing the organic carbon fraction, (iv) applying different types of mixtures of surfactants, and (v) explaining sorption hysteresis in desorption studies based on either continuous and successive washing steps. It turned out that only the IM model was able to explain the reported sorption phenomena. We also show that when one interaction is dominating, e.g. non-polar over ionic-polar, the Δ_sG of the IM model can be approximated by the sum of the different Δ_sG⁰ values, the Δ_sG of the DM model. The exact partition coefficient, K_p(C_w) (L kg^-1) = dC_s (mmol kg^-1)/dC_w (mmol L^-1), is turning each sorption isotherm into a partition isotherm that provides the K_p values required in environmental risk assessment models.

Benzalkonium ion sorption to peat and clays: Relative contributions of ion exchange and van der Waals interactions

Due to their use in various domestic and industrial formulations, benzalkonium compounds have been isolated in many environmental matrices. Sorption to soil components has been shown to play a key role in their environmental fate. Whereas sorption of benzalkonium compounds to soils is attributed to cation exchange and van der Waals forces, the relative contributions of these two mechanisms at environmental levels have not been clearly defined. In this study a previously reported algal toxicity assay-based method was employed to determine the distribution coefficients (K_d) of benzalkonium compounds between water and soil components, at environmental concentrations. Cation exchange capacity corrected K_d values for organic matter and clays were all within one order of magnitude. This implies that ion exchange is the dominant mechanism of sorption for benzalkonium compounds. When the sorption data were used to compute sorption energies for four homologues of benzalkonium ions, the magnitude of the free energy change of sorption increased with size of the molecule. The increase in sorption energy could be partly explained by increased energy of hydration with addition of methylene groups to the alkyl chain. A model that predicts sorption coefficients of benzalkonium compounds to soils using organic carbon content and cation exchange capacity was also defined. When tested using an artificial soil, the model estimates were all within one order of magnitude of the experimental values.

A review on the application of chemical surfactant and surfactant foam for remediation of petroleum oil contaminated soil

Soil, exposed to petroleum oil contaminants (in the form of petrol, diesel, gasoline, crude oil, used motor oil), may cause potential damage to the environment, animal and human health. In this review article, mechanisms of the petroleum oil contaminant removal from soil by chemical surfactant systems such as surfactant solution, surfactant foam and nanoparticle stabilized surfactant foams are explained. Laboratory based research works, reported within the last decade on the application of similar systems towards the removal of petroleum oil contaminant from the soil, have been discussed. It is an important fact that the commercial implementation of the chemical surfactant based technology depends on the environmental properties (biodegradability and toxicity) of the surfactants. In recent times, surfactant foam and nanoparticle stabilized surfactant foam are becoming more popular and considered advantageous over the use of surfactant solution alone. However, more research works have to be conducted on nanoparticle stabilized foam. The impact of physicochemical properties of the nanoparticles on soil remediation has to be explored in depth.

Application of an algal growth inhibition assay to determine distribution coefficients of benzalkonium ions between kaolinite and water

Benzalkonium compounds are widely used and found in environmental samples. Due to their amphiphilic nature, it is important to know sorption coefficients to account their bioavailability. However, currently available models describing their partitioning were developed using low molecular weight homologues and it cannot be ascertained whether they are applicable to their higher molecular weight homologues. Reasons for the scarcity of data on highly sorptive compounds include the lack of reliable quantification techniques for analyzing these chemicals at environmentally relevant levels. This study, therefore, reports on an algal growth inhibition assay-based method for the determination of kaolinite/water distribution coefficients for benzalkonium compounds at their environmentally relevant concentration range. Sorption to clay was computed using the difference between median effective concentration determined in a culture with kaolinite and that derived from a culture grown in standard medium. A kinetic model was used to account for uptake into algal cells and to calculate free concentrations. Due to the sensitivity of the algal species, Pseudokirchneriella subcapitata, it was possible to determine distribution coefficients below micromole per liter concentrations. The computed distribution coefficients showed a linear increase with number of carbon atoms in the alkyl chain up to 14. The proposed bioassay-based method should be applicable to determine distribution coefficients for highly hydrophobic chemicals and ionic liquids at a concentration range lower than typical analytical limits.

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500 °C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Effect of an eco-friendly o/w emulsion stabilized with amphiphilic sodium alginate derivatives on lambda-cyhalothrin adsorption-desorption on natural soil minerals

The effects of amphiphilic O/W emulsions, stabilized by the alkyl polyglycoside (APG) or cholesterol-grafted sodium alginate (CSAD)/APG systems, on lambda-cyhalothrin adsorption/desorption mechanisms on natural soil minerals (i.e., illite and kaolinite) were investigated. Sorption and desorption of lambda-cyhalothrin onto soil minerals was studied via batch equilibration to give insight into the adsorption equilibrium, kinetics, and thermodynamics of lambda-cyhalothrin adsorption onto minerals. The results indicate the following: (i) The adsorption processes for the APG system and CSAD/APG system include: rapid adsorption, slow adsorption, and adsorption equilibrium. The adsorption kinetics of pesticide on illite and kaolinite are in accordance with the Ho and McKay model, and the adsorption isotherm conforms to the Freundlich model. In addition, the adsorption processes of pesticide for the two systems on minerals were spontaneous and feasible (ΔG⁰ < 0), endothermic (ΔH⁰ > 0), and mainly involved chemical bonding (ΔH⁰ > 60). (ii) The equilibrium adsorption percentages of the pesticide on illite for the APG system and CSAD/APG system were 42.4% and 64.8%, and the corresponding equilibrium adsorption percentages on kaolinite were 40.8% and 61.8%, respectively. Moreover, the pesticide adsorption rate K_2-CSAD/APG was faster than K_2-APG, and its adsorption capacity K_f-CSAD/APG was greater than K_f-APG. Meanwhile, the pesticide desorption K_fd in the CSAD/APG system was smaller than that in the APG system. As a result, this eco-friendly O/W emulsion based on amphiphilic sodium alginate derivatives might provide a green pesticide formulation, since it could reduce the amount of lambda-cyhalothrin entering aquatic systems to threaten non-target fish and invertebrate species.

Adsorption of Anionic Surfactants onto Alumina: Characteristics, Mechanisms, and Application for Heavy Metal Removal

We investigated adsorption of anionic surfactants, sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS), onto alumina (Al2O3) with large size in the present study. The effective conditions for SDS and STS adsorption onto Al2O3 were systematically studied. The conditions for SDS and STS adsorption onto γ-Al2O3 were optimized and found to be contact time 180 min, pH 4, and 1 mM NaCl. Adsorption of both SDS and STS onto large Al2O3 beads increased with an increase of ionic strength, demonstrating that the adsorption is controlled by electrostatic attraction between anionic sulfate groups and positively charged Al2O3 surface, as well as hydrophobic interactions between long alkyl chains of surfactant molecules. Nevertheless, the hydrophobic interaction in terms of STS adsorption is much higher than that of SDS adsorption. The obtained SDS and STS adsorption isotherms in different NaCl concentrations onto Al2O3 beads were fitted well by two-step adsorption. Adsorption mechanisms were disused in detail on the basis of adsorption isotherm, the change in surface charge, and the change in functional surface groups by Fourier-transform infrared spectroscopy (FTIR). The application of surfactant adsorption onto Al2O3 to remove cadmium ion (Cd2+) was also studied. The optimum conditions for Cd2+ removal using surfactant-modified alumina (SMA) are pH 6, contact time 120 min, and ionic strength 0.1 mM NaCl. Under optimum conditions, the removal efficiency of Cd2+ using SMA increased significantly. We demonstrate that SMA is a novel adsorbent for removal of Cd2+ from aqueous solution.

Sorption of cationic organic substances onto synthetic oxides: Evaluation of sorbent parameters as possible predictors

Knowledge on the sorption behavior of cationic organic substances in aquatic systems is vital for their risk assessment due to the increasing detection of such chemicals in the hydrosphere. Their sorption behavior is strongly influenced by sorption processes onto mineral surfaces (e.g., oxides, clays). To contribute to the development of prediction tools, the impact of sorbent characteristics on the sorption strength was studied in a highly-idealized model system. In addition to the properties of the solid phase, the concentration of other ions in direct competition for sorption sites and the molecular structure of the sorbate were changed to separate ion exchange and non-ion exchange processes. The study includes in total 120 systematic column experiments using five extensively characterized synthetic oxides (three silica gels, two aluminum oxides), three probe molecules (two structurally related cationic substances, one neutral compound), and four distinctively different NaCl concentrations. The results show that the concentration of OH groups on the sorbent surface is a meaningful descriptor for the observed variations in sorption capacity onto different oxides. Compound-specific linear correlations were obtained, enabling the prediction of sorption coefficients. In addition, a more complex sorption behavior of organic cations compared to uncharged molecules were observed as demonstrated by the sorption results at different electrolyte concentrations. Thus, the study provides an important step towards a better principal mechanistic understanding of organic cation sorption. However, further work using other sorbents including natural ones and other probe molecules is needed to verify the identified relationships within the scope of developing reliable prediction models for cation sorption.